This project concerns the mechanisms by which extracellular signals are received by cells, with emphasis on the biochemical events involved in the transmission of such signals across membranes. During this reporting period, we have continued to study the interaction of hormones/neurotransmitters with their receptors in mammalian cells in culture. The inducible beta-adrenergic receptors in HeLa cells, which we previously described, were used to study the components of the receptor-adenylate cyclase system. In addition, the phenomenon of agonist-induced desensitization was examined, and evidence presented for a functional role for phospholipids in the domain of the receptor. Finally, new methods which permit the cultivation of rodent embryo neurons have been adapted; CNS-type receptors for diazepam (valium) were demonstrated on these cells, and new results on the nature of these receptors were reported.